One type of molding apparatus which is used to form, or example, thermoplastic pipe comprises a plurality of mold parts which move around an endless track to and from a product forming mold tunnel. It is important to control the temperature of the mold tunnel in order to control the accuracy of the product formed in the tunnel. The product itself enters the tunnel at a very high temperature and it is critical that the temperature be lowered to the point that the product is stable as it emerges from the tunnel. One way of controlling the temperature through the tunnel is through the provision of cooling liquid fed to the mold block parts as they travel through the molding tunnel.
U.S. Pat. No. 4,492,551 issued Jan. 8, 1985 to Hegler describes a molding apparatus in which two sets of mold block sections are mounted to side by side endless chains supported by a mold bed. Each set of mold block sections includes liquid cooling channels opening at the underside of each mold block section. The bed is provided with a liquid supply along the mold tunnel which feeds up and into the channels in the mold block sections while they travel through the mold tunnel.
It is important that the flow of cooling liquid be controlled and it should not leak from the mold block sections while they are travelling around the mold apparatus. In the particular Hegler structure described above, the bed itself provides a seal against leakage. Each channel has a blind upper end and is only open at its lower end. The channels do not extend between mating mold block sections thereby limiting the flow of cooling liquid from each channel to its respective mold block section and requiring separate liquid feeds for each channel. As the mold block sections leave the mold tunnel, the bottom opening channels are sealed by the bed itself.
There are currently available, other types of travelling mold apparatus which do not use a supporting bed and are therefore not limited to travelling in a horizontal plane. For example, there is currently available one type of molding apparatus which comprises first and second vertically stacked endless tracks of mating mold block sections which meet between the two tracks to form a moving mold tunnel. Another such apparatus is one in which hinged mold block sections move around a single endless track and close with one another on one side of the track to form a moving mold tunnel. Neither of these apparatuses could be fitted with the cooling channels of the Hegler structure because they do not have a supporting bed for supplying cooling liquid to the cooling channels and for sealing off the cooling channels when they are away from the mold tunnel.